This invention pertains to moisture-detecting, switching devices, and methods of forming the same, such as are used in the stator housings of electrically-driven pumps, mixers, and the like, to detect water intrusion and either to signal such intrusion or to shut off the pumps or mixers before their motors are damaged, and in particular to an improved moisture-detecting, switching device, and method of forming the same.
Typically, electrically-driven devices, such as pimps, mixers and such, comprise three main components: driving unit (i.e., the electric motor), a sealing unit, and a hydraulic unit. The first and last units are connected via a driving shaft which transmits the torque from the rotary part of the electric motor to the impeller, propeller, or whatever is the working element of the device, in the hydraulic unit.
In order to prevent the hydraulic medium from entering the electric motor, by migration thereof along the driving shaft, there is provided one or several shaft seals between the hydraulic unit and the driving unit. A commonly used seal type is the so-called mechanical face seal which comprises a rotary seal ring, and a fixed seal ring, in which the two rings are pressed towards each other by a biasing force.
As such an aforesaid seal is arranged between a driving unit and a hydraulic unit, it will operate with the fluid, i.e. water, on one side thereof, and another medium, i.e., air in the electric motor, on the other side. There is always a certain risk that the fluid, which is pressured, will enter between the surfaces of the sealing rings and get into the motor. This is especially true when dealing with heavily polluted liquids; solid bodies in the fluid may enter between the sealing surfaces and cause such damage that a heavy leakage can ensue.
In order to provide a more secure sealing between the driving unit and the hydraulic unit, it is known to arrange a dual mechanical seal which confines an oil chamber therebetween. The seal between the oil chamber and the motor, then, will perform efficiently, as the oil, normally, will not contain any solid bodies. In addition, each of the seals is subject to a considerably lower pressure difference. Against the possibility of water entering the oil chamber, the oil is checked at prudent intervals, and is changed when and as necessary.
Such sealing arrangements notwithstanding, if water should get into the motor housing, it is important that this event be noticed immediately, before the water causes any damage to the electric windings. In such circumstances, it is desirable that the motor current be cut off, and an alarm generated, before any serious damage has occurred.
Devices for interrupting current circuits, and for generating an alarm, if a liquid has entered a given space are known.
German patent specification No. 321 314 shows a device in which electric contacts are parted by a body which is dissolved in water. A disadvantage with this arrangementis that the dissolution of the body takes place only gradually, consequently it cannot be used for strong current. U.S. Pat. No. 4,133,016 discloses a device in which a switch is controlled by a disc made of only water-soluble material, The disadvantage, here too, is that the release is too slow.